1. Field of the Invention
This invention relates to a conveyor means using linear motors for conveying articles.
2. Description of the Prior Art
From the viewpoint of increasing the production efficiency and improving the working environment, it has recently been desired at the production line of manufacturing plant to convey articles speedily and silently. As the conveyor means to meet such requirement, it has been known to provide a linear motor comprising linear coils and reaction members at each working station of the production line and to pass on an article to the succeeding working station by the linear motor.
The conveyor means using linear motors as mentioned above has the following construction.
As shown in FIG. 26, for example, either of linear motor coils b and a reaction member c comprising a linear motor a (linear motor coils b in the case of FIG. 26) is made a stator or fixed element, which is arranged below and along a roller conveyor e comprising a plurality of rollers d. The other (reaction member c in the case of FIG. 26) is made a rotor or moving element, which is fitted to a pallet f (which is conveyed) through the medium of a fitting member g. By thrust F which is generated at the rotor (reaction member c) due to electromagnetic action between the linear motor coils b and the reaction member c, the pallet f and an article placed thereon are conveyed through the medium of the rotor (reaction member c).
In the conveyor means using linear motors of this kind, as disclosed by the Japanese Patent Application Laying Open Gazette No. 62-210162, for example, a controller is provided for a linear motor of each working station and when a pallet is conveyed between adjoining stations, which the first half part of conveyance is controlled by a controller corresponding to the working station on the upstream side in the conveying direction, the latter half part is controlled by a controller corresponding to the working station on the downstream side in the conveying direction.
In the above conventional control system, there is caused a sphere which is entirely outside the control by a controller in the course of conveying and as shown in FIG. 25 by broken lines, the conveying speed V becomes easy to vary in that sphere, with the result of bad influence upon deceleration control, reduction in precision of stop position and decrease in transporting efficiency.
Also, in the above conventional control system, the speed control on a transporting pallet on each working station is done entirely by a controller and the control on the transfer of a transporting pallet between adjoining working stations is carried out by exchange of signals between an overall controller and a controller. Therefore, in the case of actual conveying, a transporting pallet must be conveyed while the controller is exchanging signals with the overall controller at all times. Thus, control is complicated and satisfactory reliability cannot be obtained. Moreover, since it is so designed that control on a carrier existing at each unit is done by the controller, even in case of emergency when the carrier must be stopped suddenly, the carrier stops only after a signal is given to the controller from the overall controller. Thus, due to delayed control, the carrier cannot be stopped instantly in case of emergency.
In sending an article to a plurality of working stations in regular sequence by using a linear motor, in the case where adjoining articles are conveyed at the same time or in the case where conveying of an article on the rear side is started while an article on the front side in the conveying direction is being conveyed, there is a fear that the articles collide with each other because the space between adjoining working stations is short and transporting speed is very high.
In order to prevent collision of articles during conveying, a conveyor mans ( for example, the Japanese Patent Application Laying Open Gazette No. 60-237803), by which after an article on the front side is conveyed, it is confirmed that such article does not remain in the conveying area of an article on the rear side and then conveying of the article on the rear side is started, has been suggested.
In the above conveyor means, however, delay in conveying of articles on the front side will accumulate at the transportation of articles on the rear side, with the result that time required for transporting at the production line as a whole increases and in its turn, transporting efficiency or production efficiency will lower.
A main object of the present invention is to provide a conveyor means using linear motors which ensures stabilized conveyance by controlling transportation of articles between adjoining stations at all times by one controller. In order to attain this object, in the present invention a linear motor for conveyance comprising linear motor coils and a reaction member is provided at each station of the transporting line (having a plurality of stations) and one controller is provided for every two adjoining stations so as to control the working of two corresponding linear motors for conveyance when articles are conveyed by said two corresponding linear motors between adjoining stations. Thus, conveyance of articles by the linear motor is always controlled by the controller, with the result of stabilization of transportation control, improvements of stop position precision and transporting efficiency, etc.
In the present invention, in order to carry out the transfer of a transporting pallet between adjoining working stations reliably and easily, the controller is provided with a sequence controller which effects the speed control on linear motors for conveyance of two adjoining working stations. The controller is also provided with a linear motor controller which controls linear motors for conveyance. While the sequence controller controls the transporting line through the medium of the linear motor controller, the linear motor controller carries out phase control of linear motor excitation.
Under the above construction, the sequence controller carries out control on the speed of the linear motor between adjoining working stations and the linear motor controller carries out phase control of the linear motor (linear motor coil) excitation. Thus, transfer of a transporting pallet between two working stations is carried out smoothly and easily, without signal output from the linear motor controller to the sequence controller and without complication of control. Also, since the sequence controller monitors only adjoining stations, even if trouble occurs at a certain station, conveyance at other stations can be carried out.
In the case where adjacent articles are conveyed at the same time or in the case where conveying of an article on the rear side in the conveying direction is started while an article on the front side in the conveying direction is being conveyed, there is a fear that articles collide with each other. In order to prevent such collision and thereby improve transporting efficiency by changing the transporting speed of articles in transportation properly, the present invention provides a conveyor means using linear motors, having a control means to control working of linear motors for conveyance, a position detecting means to detect the actual positions of adjoining articles in transportation and a correcting means to correct the transporting speed of at least one of adjoining articles under control by said control means on the basis of a signal given by said position detecting means so as to keep the space between adjoining articles at more than a specific value. In this conveyor means, after completion of work at the working station adjoining articles are so controlled that they are conveyed at the same time or so controlled that conveying of an article on the rear side is started while an article on the front side in the conveying direction is being conveyed. In the present invention, therefore, in the case where an article approaches abnormally to an adjoining article from a certain cause when it is being conveyed at a predetermined set speed between adjoining working stations on the basis of the control by a control means which controls working of a linear motor, this phenomenon is detected by a position detecting means and on the basis of the result of detection, a correcting means corrects the conveying speed of at least one of the adjoining articles under control by said control means, whereby the space between adjoining articles in transportation is kept at more than a specific value. Thus, collision of articles with each other is prevented and transporting efficiency can be improved.
In order to eliminate the delayed control and to ensure instant stop in case of emergency, the present invention has for its object to provide a conveyor means using linear motors, having the controller provided with a linear motor controller to control linear motors for conveyance and a station controller to control the transporting line through the medium of said linear motor controller, whereby control on the linear motor under normal condition is done by the linear motor controller but in case of emergency a stop signal is outputted directly to a linear motor from the station controller.
Therefore, under normal conditions control of the linear motor is done by the linear motor controller but in case of emergency the linear motor is controlled directly by the station controller and a stop signal is outputted without delay to the linear motor. Thus, delayed control is eliminated and a transporting pallet (article in transportation) can be stopped instantly.
In order to avoid a longer time required for transporting all articles and to save consumption energy, the present invention provides a conveyor means using linear motors, having a controller which is so composed that it sends articles to a plurality of working stations in regular sequence by using a linear motor, a fixed speed area detecting means to detect the article transporting fixed speed area of each station and an acceleration control means to effect acceleration for transporting articles of a specific station upon receiving output of said fixed speed area detecting means at the article transporting fixed speed area of the station preceding said specific station. Thus, in each station, acceleration for article transporting is effected at the article transporting fixed speed area of the station preceding said each station, whereby a longer time required for transporting all articles can be avoided and consumption energy can be saved.